How to model glass with octogonal base and cylindrical top?
I'm not completely sure about the transition between the sharp faces and the circular part but basically you can try it this way:
Create a 8 vertex circle, subdivide it 7 times:

Keep only 1/8, array it around an empty:

Extrude up:

Create the mid-edge, apply the Array, round the top edge with LoopTools &gt; Circle:

Create another edge, round it with LoopTools &gt; Circle:

Begin to scale the edge loops, add some new ones:

Here is what it gives: